It is well known to secure cargo containers by the use of mechanical seals. The purpose of using seals is two fold, namely, to prevent, or at least render difficult, breaking into cargo containers, and to make sure that any such attempts do not go undetected.
The simplest type of such mechanical seals includes a steel bolt composed of a shank with a shank head formed at one end and a free end adapted for locking engagement with a locking element. A typical PRIOR ART seal is seen in FIG. 2. In use, the bolt is positioned so as to pass through the hasp of a container locking mechanism, thereby to prevent opening of the locking mechanism without breaking the seal. Over the years, such seals have become increasingly sophisticated, and have advanced so as to include means for indicating an attempt at tampering with or removing the seal, such as disclosed in U.S. Pat. No. 5,005,883 to Guiler.
A significant problem with cargo container seals is that most attempts at pilfering or break in occur during transportation or transfer of the cargo containers, and even if a break in is seen to have happened, it will often be a long time after the event, and it is generally not possible to prevent such break ins, to catch perpetrators, or even to identify the location and timing of the break in.
There have also been developed electronic tagging devices such as those which include a digital data memory, in which is stored data pertaining to the cargo container and its contents. Such devices are typically RFID devices which are remotely interrogatable. Advantages of electronic tagging devices is that they enable relatively easy, electronic inspection of a large number of containers, and, if connected to a central control center, they also can enable real time knowledge of attempted break ins.
U.S. Pat. No. 6,265,973 to Brammall et al., entitled Electronic Security Seal (the '973 patent), discloses a seal in which an insulated electrically conductive bolt is adapted for locking together with a locking mechanism so as to complete therewith an electrical circuit connected to electronic apparatus which is adapted to generate a tamper evident RF signal if the bolt is removed or severed. The bolt/locking mechanism interface must be specially sealed so as to prevent the ingress of moisture into the electronics.
Advantages of employing RFID devices in conjunction with electronic seals include the ability to interrogate multiple cargo containers or other secured objects, simultaneously and remotely.
As an omni-directional communications medium, RF technology is far superior for many purposes than various line of sight media, such as infrared, as the latter requires—by definition—an unobstructed and substantially direct line of sight, and a single signal receiver is able to receive signals from a single transmitter only.
However, the use of RFID devices in the protection of cargo containers, trucks, and other security and tracking applications, has a number of disadvantages, including the simultaneous reception of multiple potentially overlapping and garbled messages by a single interrogator device, as discussed in the above-referenced '973 patent. Furthermore, notwithstanding the fact that RF signals may be encoded, it is nonetheless possible for unauthorized persons to intercept such signals, thereby compromising the security of the cargo.
It is also known to use ultrasound technology, for the tracking of people or objects within enclosed areas such as buildings. Ultrasound is far less useful medium than RF, however, requiring an angular ‘field’ of view, and being poorly conducted in air such that receivers must be placed within a short range. It does possess, however, the advantage of not causing electronic interference with computer systems, including sensitive medical instruments. Accordingly, it is worth ‘paying the price’ when it comes to tracking systems in hospitals, office premises, and other enclosed locations in which tracking of small objects and people may be highly desirable, but wherein RF systems are impractical.
Representative of prior art uses of ultrasound technology for purposes such as mentioned above, are the following:
U.S. Pat. No. 3,439,320 entitled Personnel Location System. This document relates to a system in which each of a plurality of persons whose location is to be ascertained carries a transmitter that produces an ultrasonic sound signal having a unique frequency. Each room or area to be designated has an ultrasonic receiver or transducer capable of sensing any of the unique frequencies within its range. The ultrasonic transducers in the different areas are all coupled to a display panel capable of indicating the designated areas and each person to be located. When a person actuates his transmitter in one of the areas, an indication is given on the control panel of the location of this person at a designated area. Preferably, the indication is maintained until the person moves to a different area and actuates his transmitter there.
U.S. Pat. No. 3,696,384 to Lester, entitled Ultrasonic Tracking And Locating System. This document discloses an ultrasonic tracking and locating system in which an identification code number is programmed on a console keyboard to activate an encoder which transmits a plurality of coded pulses to a plurality of transceiver units located in the rooms of a building where surveillance is desired. A transducer in the transceiver transmits a coded, ultrasonic digital signal which is dispersed throughout the room. Portable pocket unit transceivers carried by persons to be located receive the transmitted ultrasonic signals and decode the signals to determine if they correspond to the pocket unit's identification code. If the signal corresponds to the pre-programmed code, the pocket unit transmits a single ultrasonic pulse which is received by the room transceiver and is transmitted back to the console, where a display converter activates a digital readout display to provide a visual, numerical indication of the location of the person.
U.S. Pat. No. 4,225,953 to Simon et al., entitled Personnel Locator. This document discloses a personnel locator and display system for indicating on a status board the room numbers where designated key individuals are located at a given moment. Small portable transmitters, either ultrasonic or radio frequency, are worn by the key individuals, and receivers are provided in the rooms. The various transmitters emit pulses according to a preprogrammed timing sequence, and a decoding logic network connected to receiver signals received in the rooms identifies the specific transmitter and room number and displays same on a status board. A programmer-recharger unit programs the pulse timing for each transmitter for identification of the wearer.
U.S. Pat. No. 4,367,458 to Hackett, entitled Supervised Wireless Security System. This document discloses an ultrasonic communication system capable of wireless installation and supervised operation is achieved by communicating each information bit as two distinct ultrasonic frequencies separated in frequency enough to assure that the signal strength of both transmissions will not be in a deep null at the receiver location at the same time. The transmissions can be coded with a format that recognizes the correct data transmission even if reception of one frequency is lost. By use of transponders and other auxiliary units with periodic polling, supervised operation throughout a building can be maintained with events such as intrusion, fire or emergency as well as failures of particular units of the system reported.
U.S. Pat. No. 4,955,000 to Nastrom, entitled Ultrasonic Personnel Location Identification System. This document discloses an ultrasonic system for identifying the location of personnel within a multiple room complex. The system includes ultrasonic transmitters adapted to be transported by the personnel. The transmitters periodically transmit pulse code modulated (PCM) transmitter signals representative of a digital code sequence characteristic of the person, and formed by a plurality of bit positions which are separated from adjacent bit positions by predetermined time intervals. Ultrasonic receivers for receiving the transmitter signals are positioned within each room of the complex. The receivers detect bits of the code sequence only during window periods corresponding to expected bit positions. Detected code sequences are compared to predetermined code sequences, and receiver signals are produced as a function of the comparison. A central station is coupled to receive the receiver signals, and provides a visual indication of the rooms in which the persons transporting the transmitters are located.
U.S. Pat. No. 5,218,344 to Ricketts, entitled Method And System For Monitoring Personnel. This document discloses a method and system for monitoring personnel in an institution such as a correctional facility, hospital, school, military installation, and the like. The system includes a computer connected with one or more stationary transceivers in a defined area of the facility, and a portable transceiver unit worn by each individual who is to be monitored. The computer sends command signals to the stationary transceivers, which broadcast interrogation signals to the portable units. The portable units are configured to respond only to interrogation signals unique to that individual, and upon decoding an interrogation signal incident thereon, broadcast a response signal to the stationary transceivers. The stationary transceivers relay corresponding data to the computer, where the data is analyzed to provide an indication of the number, location and identity of the individuals. The portable transceiver units have an emergency alarm button which may be actuated by the individual in the event of an emergency, and selected portable transceiver units may also be configured to be sensitive to proximity between them. In addition, the portable units may be coded for access to vending apparatus.
U.S. Pat. No. 5,245,317 to Chidley et al., entitled Article Theft Detection Apparatus. This document discloses a method and system for monitoring an item within a defined area and sounding an alarm if the item is removed from the area. A transmitter and transducers emit ultrasound which substantially saturates the area to be monitored. A security tag having a detector and alarm is attached to the items to be monitored within the area. Sensing circuits may be additionally provided to determine whether a security tag is being tampered with or removed by an unauthorized person. The security tag's alarm is sounded in the event that the receiver does not detect the ultrasound indicating that the monitored item is no longer in the monitored area. Additional alarms may be provided for indicating that the security tag has been tampered with or removed.
U.S. Pat. No. 5,708,423 to Ghaffari et al., entitled Zone-Based Asset Tracking And Control System. This document discloses a data processing system which automatically maintains records of respective locations of a plurality of objects in real time. Each of the objects has secured thereto a respective object marker which transmits an identification signal that is unique to the respective object. Sensor devices are installed at respective doorways of a building. Each sensor device receives the identification signal transmitted from the object marker as the respective object is moved through the doorway. The sensor device detects from the identification signal a direction in which the object is being moved through the doorway and generates a detection signal indicative of the detected direction of movement and also indicative of the identification signal for the object. The data processing system receives the detection signals from the sensor devices and maintains a data record with respect to each of the objects indicating the present location in the building of each of the objects.
U.S. Pat. No. 6,433,689 to Hovind et al., entitled System For Supervision And Control Of Objects Or Persons. This document discloses a system for supervision and control of objects or persons within a limited area, such as a building, comprising a plurality of electronic identification chips for placing on respective objects/persons to be supervised/controlled, each chip having stored therein a special ID code and being provided with respective transmitters and receivers for communication via ultrasound as well as audible sound, a plurality of stationary detectors which are interconnected in a network and arranged for two-way communication with the chips, and a central control unit in communication with the chips via the detectors. Each chip is continuously active in operation and is arranged to transmit its ID code at predetermined time intervals. At least one of the detectors or the control unit are arranged to trigger an alarm unit if an incorrect code is received or an approved code is not received continuously at predetermined time intervals.
U.S. Pat. No. 7,061,381 to Forcier et al., entitled Ultrasonic Transmitter And Receiver Systems And Products Using The Same. This document discloses a transceiver preferably embedded within a wearable security watch, PDA, or other device which achieves a variety of wireless ultrasonic and/or radio-frequency based functions, including digital identification and proximity and sensation monitoring of assets, individuals, pets, and the like. The portable or wearable device realizes these functions by periodically polling and receiving information tags within the transmitting distance of the device. The invention can help reduce the likelihood of the theft, loss, or misplacement by detecting that a tag associated with or attached to an entity has left an individual's proximity and sounding an alarm. The device can also assist individuals with sensory impairments, including persons who are deaf, diabetic, and the like, by detecting a tagged entity as it enters the space around an individual, or by detecting environmental stimuli, such as excessive heat in an individual's proximity or vital sign changes, and sounding an alarm.
The use of ultrasound technology has thus found applicability in certain indoor environments, or for uses which require very close contact between items to be monitored, and on an ad hoc, limited basis.